The present invention relates to a magnetic recording medium employed in an apparatus such as a magnetic disk apparatus; a process for producing the magnetic recording medium; a sputtering target employed for producing the magnetic recording medium; and a magnetic recording and reproducing apparatus comprising the magnetic recording medium.
Conventionally, a metallic substrate formed of, for example, an aluminum alloy is widely employed as a substrate for producing a magnetic recording medium. Usually, such a metallic substrate undergoes texturing, and is employed for producing a magnetic recording medium.
Texturing is a process for forming an irregular surface on a substrate along a predetermined direction (usually in a circumferential direction) of the substrate. When the surface of a substrate undergoes texturing, the crystalline orientation of an undercoat film and a magnetic film, which are formed on the substrate, is enhanced, and the magnetic film exhibits magnetic anisotropy. Thus magnetic characteristics, such as thermal stability and resolution, of a magnetic recording medium can be enhanced.
In recent years, instead of a metallic substrate formed of aluminum or similar metal, a non-metallic substrate formed of material such as glass or ceramic has been widely employed as a substrate for producing a magnetic recording medium. Such a non-metallic substrate has an advantage that head slap does not easily occur in the substrate, because of the high hardness of the substrate.
However, in the case in which a non-metallic substrate such as a glass substrate is employed, the magnetic film may not be imparted with satisfactory magnetic anisotropy even when the substrate undergoes texturing. As a result, the resultant magnetic recording medium may exhibit unsatisfactory magnetic characteristics.
In order to solve such problems, formation of a hard film which can be easily textured on a non-metallic substrate formed of material such as glass or ceramic has been proposed.
For example, Japanese Patent Application Laid-Open (kokai) No. 5-197941 discloses a magnetic recording medium including a non-metallic substrate formed of material such as glass or ceramic, and the substrate is coated through sputtering with NiP film serving as a hard film which is easily textured.
Japanese Patent Application Laid-Open (kokai) Nos. 4-29561 and 9-167337 disclose a magnetic recording medium including a non-metallic substrate which is plated with film such as electroless plating film, and the film serves as a hard film.
A magnetic recording medium including a hard film formed on a non-metallic substrate is produced through the following process: the hard film is formed on the substrate in a film formation apparatus such as a sputtering apparatus; the substrate is temporarily removed from the apparatus and is subjected to texturing by use of a texturing apparatus; the resultant substrate is again placed in the apparatus; and then an undercoat film and a magnetic film are formed on the substrate.
However, the aforementioned conventional production process for a magnetic recording medium includes complicated production steps, resulting in high production costs. Therefore, there has been keen demand for a production process for a magnetic recording medium, which encompasses a simplified production procedure.
In view of the foregoing, an object of the present invention is to provide a process for easily producing a magnetic recording medium exhibiting excellent magnetic characteristics.
The present invention provides a process for producing a magnetic recording medium characterized by forming an orientation-determining film, which determines the crystalline orientation of a film provided directly on the orientation-determining film, on a non-metallic substrate which has undergone texturing; subjecting the orientation-determining film to oxidation or nitridation; and forming a non-magnetic undercoat film and a magnetic film on the orientation-determining film.
The oxidation or nitridation is carried out by bringing the orientation-determining film into contact with an oxygen-containing gas or a nitrogen-containing gas.
The present invention also provides a process for producing a magnetic recording medium, which comprises forming an orientation-determining film, which determines the crystal orientation of a film provided directly on the orientation-determining film, on a non-metallic substrate which has undergone texturing; and forming a non-magnetic undercoat film and a magnetic film on the orientation-determining film, wherein the orientation-determining film is formed through sputtering by use of a sputtering gas containing nitrogen or a sputtering gas containing oxygen.
Preferably, the orientation-determining film comprises NiP (the content of P is 10-40 at %) as a primary component.
Preferably, the orientation-determining film comprises NiPX (wherein X is one or more species of Cr, Mo, Si, Mn, W, Nb, Ti, and Zr, and the content of X is 0-25 at %) as a primary component.
The present invention also provides a sputtering target for forming the orientation-determining film, which comprises NiPX (wherein X is one or more species of Cr, Mo, Si, Mn, W, Nb, Ti, and Zr, and the content of X is 0-25 at %) as a primary component.
The present invention also provides a magnetic recording medium comprising a non-metallic substrate which has undergone texturing; an orientation-determining film formed on the non-metallic substrate; and a non-magnetic undercoat film and a magnetic film, which are formed on the orientation-determining film, characterized in that the ratio of a coercive force in a circumferential direction of the medium (Hcc) to a coercive force in a radial direction of the medium (Hcr); i.e., Hcc/Hcr, is 1.1 or more.
The orientation-determining film has an average surface roughness (Ra) of less than 0.5 nm.
The magnetic recording medium of the present invention comprises a structure wherein a non-magnetic adhesive film, which prevents exfoliation of the orientation-determining film from the substrate, is formed between the non-metallic substrate and the orientation-determining film, and the non-magnetic adhesive film comprises one or more species of Cr, Mo, Nb, V, Re, Zr, W, and Ti.
The present invention also provides a magnetic recording and reproducing apparatus comprising the magnetic recording medium and a magnetic head for recording data onto the medium and reproducing the data therefrom.